1. Field of the Invention
The present invention relates in general to a telecommunication network and a method of controlling the switching of a telecommunication signal in a telecommunication network. More particularly, the present invention relates to the control arrangement for controlling the switching of a telecommunication signal in a telecommunication network.
2. Related Art
In a modern telecommunication network there is a need to provide flexible call control architectures of the switched networks to facilitate the implementation of new features and services. Networks which provide such flexibility have been termed `intelligent networks` and are discussed in detail in "Intelligent Networks" by Jan Thorner (Artech House. Boston. London).
A typical intelligent network is illustrated in FIG. 1. In such a network when a local exchange 1 receives a telecommunication signal from a telephone 2, the signal is interpreted by the call control function (CCF). Limited processing of the telecommunication signal can take place within the service switching function (SSF). However, if more advanced processing is required the SSF has the ability to generate a query i.e. a request for control from a centralised transaction processor termed the service control function (SCF). The query from the SSF is passed initially to a signalling transfer function which routes the query to the required SCF. The SCF is a centralised transaction processor which hosts advanced services controlled software termed service logic programs (SLPs) or applications. When an SCF receives a query, an application will be initiated which requires data. The application running in the SCF refers to a service data function (SDF) for the requisite data. The SCF can then return instructions to the SSF in the local exchange 1 via the STF.
The advantage of this arrangement is that the advanced services are provided at a centralised location. This enables both the applications in the SCF and the data in the SDF to be updated as desired when advanced services are to be updated. A customer is able to modify the applications for data in the SCF and SDF respectively by changing the application or data in a service management function (SMF). The SMF is able to update the applications and data in the SCFs and SDFs respectively easily in view of their centralisation location. The SMF is also able to manage the STF and SSF if required.
In order to standardise communication over intelligent networks, various standard signalling protocols have been agreed. For instance, communication between the SSFs, the STFs, the SCFs and the SDFs can be achieved using the CCITT (Consultative Council of International Telephone and Telegraph) 7 common channelling signalling network. The CCITT 7 protocol comprises a signalling connection control part (SCCP) and transaction capabilities (TCs). In addition an intelligent network application part (INAP) can be stacked on this C7 transport.
The communication of the management functions from the service management function can be carried out using an asynchronous transfer mode (ATM) X25 link which uses a file transfer protocol (FTP) for the transfer of management data e.g. for the updating of the applications and data in the SCFs and SDFs respectively.
A centralised architecture has the advantage that it provides for flexibility compared with a distributed network. It also provides savings on management network infra structure since the centralised applications and data only have to be updated for one location. In a distributed network the applications and data would need to be updated throughout the network.
The centralised network however suffers from the disadvantage that the SSF must transmit a query to a centralised SCF thus causing switching delays for the signal over the speech path.